In my case the problem was someone implemented Map<list<T1>, list<T2>>. Same case after update for .NET8 and AutoMapper 13 I encountered similar message (not too much descriptive for me).

My solution was removing the list and "assume" AutoMapper is enough smart to map the list. Map<T1, T2>

I said "assume" because I added this in the startup:

public static List<TDestination> MapList<TSource, TDestination>(this IMapper mapper, List<TSource> source)
{
   return source.Select(x => mapper.Map<TDestination>(x)).ToList();
}